A solution to the problem of identifying remote objects by radar has long been sought. The technique still being pursued with little success is that of the target-time response wherein different reflecting parts of the object at different radial distances from the transmitter are measured just as in the radar range measuring technique. Where an object may have a maximum dimension in any direction of one or two hundred feet, it can be seen that electromagnetic energy traveling at the speed of light would require extremely short pulses to obtain the necessary resolution to "see" the shape of objects of such small size. Since the speed of light is of the order of 1,000 feet per microsecond, to resolve objects 100 feet apart would require pulses of less than a few nanoseconds duration. A radar receiver, known in the prior art, intended for identifying radar targets is shown in FIG. 1 where the received nanosecond pulses of microwave energy are reduced in frequency by a local oscillator 12 in a mixer 10, are amplified at 14, detected at 16, and then processed in an extremely high bit-rate logic circuit 18.
For the system of FIG. 1 to successfully operate, the radar pulses must be extremely short in duration or pulse compression must be used, both requiring large time-bandwidth and very low phase and amplitude distortion. Such equipment is difficult to manufacture and operate. The logic circuit for processing the received pulses must have a very high clock rate or use sampling techniques to produce a reliable signature. The system of FIG. 1 poses serious operational problems also. The target of interest must be acquired, then tracked in range accurately in time within the radar's range resolution capability. No method of avoiding a human operator in the "tracking loop" exists. Rapid identification of targets using just a few radar hits from each target is not feasible because of the acquisition and tracking problem.